The clinical success of external fixation of bones has been well documented in the orthopaedic literature. However, external fixation at or near a joint can be problematic due to biomechanical requirements. For example, because the wrist has degrees of freedom which allow rotation, flexion, adduction, and abduction, external fixation near the wrist should be adjustable to ensure that proper fracture alignment is achieved. Furthermore, in order to avoid damage to the tendons and nerves that surround the wrist, the pins which are used to couple the fixation device to the body are usually placed on opposite sides of the wrist in the metacarpal bone and the radius. As a result, the fixation device must be sufficiently articulated to reduce the fracture using the forces transmitted through the wrist.
In order to address these, as well as other complications associated with fixation at or near a joint, a number of fixation devices have been developed. Examples include those disclosed in U.S. Pat. Nos. 4,554,915, 4,611,586, 4,628,919, 4,782,842, 4,919,119, 4,922,896, Re. 34,985, 5,122,140, 5,152,280, 5,304,177, 5,320,622, 5,437,667, 5,545,162, 5,601,551, 5,683,389, and 5,743,898. One particular problem common to these, as well as other prior art devices, is the need to have both large scale distraction to facilitate implantation and precisely controlled distraction to ensure proper fracture reduction. Some of these patents attempt to overcome this dilemma by requiring assembly and/or disassembly of multiple parts. U.S. Pat. No. 5,662,649 to Huebner discloses an external fixator for repairing fractures of the distal radius and wrist which allows both rapid gross distraction and finely controlled distraction without the need for intraoperative assembly or disassembly. However, the nut and thread assembly which permits both types of movement can be cumbersome to use and unintentional switching between the movement modes is possible.
As the discussion above illustrates, there is a need for an improved external fixation device for bone.